The present invention relates to an improved diaphragm type pump device which performs pumping function by the reciprocating movement of a diaphragm through a slide shaft.
FIG. 1 is a longitudinal cross-sectional view of a conventional diaphragm type pump device of this kind. In FIG. 1, a slide shaft 1 is supported by a slide bearing 14 mounted on a predetermined position of a bracket 2 to be capable of reciprocating movement. A movable plate 6 is integrally secured to the upper end of the slide shaft 1 by caulking, a flexible diaphragm 5 being secured to the movable plate 6 in an overlapping state by means of, for example, heat-bonding. A plurality of discharge valves 8, 8 are mounted on the movable plate 6. The circumferential part of the diaphragm 5 is clamped by the casing 3 connected to the bracket 2 and a cover 4 closing an opening of the casing 3, whereby the interior of the casing 3 provided with the cover 4 is sealingly partitioned into a suction chamber A and a discharge chamber B. A valve sheet 10 provided with an inlet valve 9 at its central portion is mounted at the base portion of an inlet tube 4a which is formed at the substantially central portion of the cover 4. An O-ring 15 is placed in an annular groove in the outer circumferential surface of the valve sheet 10 to keep air tightness of a fitting surface formed between the valve sheet 10 and the cover 4. A coil spring 11 extends between a spring receptacle 12 held at a predetermined position of the slide shaft 1 by means of a snap ring 13 and the lower surface of the casing 3, thereby to urge the slide shaft 1 in the downward direction. A fixing bolt 16 is provided to fix the bracket 2 and the casing 3 together.
In the conventional diaphragm type pump device having the construction as above-mentioned, when the movable plate 6 is lowered from the upper dead point as shown in FIG. 1 by a returning elastic force of the coil spring 11, the suction chamber A is rendered to be in a negative pressure condition whereby the inlet valve 9 is opened and accordingly, fluid is sucked from the inlet valve 9 into the suction chamber A. When the movable plate 6 is lowered to a predetermined position, namely the lower dead point and the movable plate 6 is raised along with the slide shaft 1 by means of, for example, a cam mechanism (not shown) against the action of the coil spring 11, pressure in the suction chamber 1 increases to close the inlet valve 9 which has been opened. Conversely, the discharge valves 8, 8 of the movable plate 6 are opened whereby the fluid inside the suction chamber A is discharged into the discharge chamber B through the discharge valves 8, 8. In the next place, the movable plate 6 is again lowered from the upper dead point as shown in FIG. 1 by the returning elastic force of the coil spring 11. Then, the discharge valves 8, 8 of the movable plate 6 which have been opened are closed and the fluid inside the discharge chamber B is discharged outside through a discharge hole 3a and at the same time, the fluid is sucked into the suction chamber A through the inlet valve 9. By repeating the operations as above-mentioned, the fluid is sucked through the inlet tube 4a and is discharged outside through the discharge hole 3a.
Since the conventional diaphragm type pump device is constructed as above-mentioned, the fluid always remains in an air gap G formed between the diaphragm 5 and the cover 4 even when the movable plate 6 reaches the upper dead point as shown in FIG. 1, on account of which efficiency of the pump device is poor. Particularly, when the diaphragm type pump device is used as a vacuum pump, an achievable degree of vacuum is low and especially, the rising characteristic of vacuum is poor.